What the Largest Structures in the Universe can tell us about the Smallest

1. What the Largest Structures in the Universe can tell us about the Smallest Edmund Bertschinger MIT Department of Physics and Kavli Institute for Astrophysics and Space Research

2. Matter particles Spin Two known types: Quarks Feel strong force Leptons Do not feel strong force Force carriers Spin Four known types: Photons Carry electromagnetic forces Gluons Carry strong nuclear force W,Z0 Carry weak nuclear force Gravitons Carry gravity (in principle) Higgs (not yet discovered) Gives matter particles mass Elementary Particles:The “periodic table” of physics Many more types are expected to be found this decade!

3. Matter particles grouped into sets Electron (stable) up quark Electron neutrino down quark Muon (unstable) charm quark Muon neutrino strange quark Tauon (unstable) bottom quark Tau neutrino top quark 1 2 3 Nature provides 3 copies for no apparent reason. In addition, every particle has an antiparticle.

4. What force carriers can do to matter particles: chemistry • Change the momentum e + g e’ + g’ (requires electric charge) • Change the particles (alchemy!) e + W+  ne (requires weak charge) • Produce matter/antimatter pairs, or be produced when matter and antimatter annihilate e+ + e-  g+g (e- = electron, e+ = antielectron) g+g  e+ + e- (Particles are not conserved!)

5. Composite particles • Mesons: quark-antiquark pairs which do not annihilate because the quarks have different strong charges Pi meson = (up + anti-up) and (down + anti-down) • Quantum superposition! • Baryons: three quarks whose strong charges add to zero Proton = (up + up + down) • Atomic nuclei: protons+neutrons • Etc.

6. Outstanding problems of particle physics Why is the periodic table so complicated? “The search for unified field theories” Supersymmetry Why are the elementary particle masses so light but not zero? “The mass problem” Higgs particle Astrophysics and cosmology are unlikely to help answer these questions.

7. Particles are not particles They’re waves! Electron microscope! No, they’re particles! Photoelectric effect No, they’re waves! Compromise: they’re wavicles! (wave packet) Sometimes “particles” behave like particles, sometimes like waves!

8. Particles are field “excitations” Electron field with no electrons: Electron field for a beam of many electrons: Electron field of a localized electron:

9. Why is astrophysics relevant? The early universe was the most powerful particle accelerator ever. Cosmic expansion has stretched wavicles whose wavelength was microscopic, to be larger than the observable universe today.

10. Dark matter after the big bang

11. The universe was denser, hence hotter, in the past Thermodynamics: compressing a gas makes it hotter, if the heat is trapped in the gas Hot gas energetic particles  many particles can be produced by collisions e.g., g+g  e+ + e-

12. Dark matter: neutralino c0 (chi-zero) Weak forces change one kind of matter particle into another e- + W+  ne (requires weak charge) Supersymmetric forces (hypothetical new forces) change matter particles into force carriers and vice-versa. Lightest supersymmetric particle, c0 , is predicted to be stable.

13. Neutralino production requires high particle energies E=mc2 is true only for particles at rest! energy E, mass m, speed of light c E2 = (mc2)2 + (pc)2 is always true momentum p=Ev/c2, speed v n + n  c0 + c0requires E(n) > m(c0) >> m(n)  produce c0 = c0in hot early universe

14. Quantum mechanics: Heisenberg uncertainty principle It’s impossible to measure both position and momentum (proportional to 1/wavelength) exactly for a wavicle It’s also impossible to measure the energy (proportional to 1/frequency) in an arbitrarily short time. These hold for any kind of wave, not just quantum wavicles!

15. The particle loophole Particles can materialize out of nothing (vacuum), live a short time, then disappear. Nothing  e+ + e-  Nothing Virtual Particles

16. Effects of virtual particles All “static” forces (gravity, electrostatic, magnetostatic, etc.) carried by virtual force-carriers Virtual particles interact with real particles to modify their interactions (“plasma screening” or “confinement”) Virtual particles contribute nonzero energy to the vacuum (empty space). The problem: they contribute Infinite energy!

17. Virtual particles in cosmology The universe has no preferred axis of orientation  spin-0 force-carriers (e.g. Higgs field) can contribute a residual nonzero energy Vacuum or “false” (temporary) vacuum energy Could explain dark energy Could also power the big bang itself!

18. Powering the big bang:Cosmic Inflation (Alan Guth, 1981) Recall from lecture 1: Separation between pair of matter particles R(t) If dR/dt > 0 and CR2 > k, eventually k becomes tiny and can be neglected to good approximation. Exponential growth of prices = inflation

19. Consequences of cosmic inflation A region smaller than a peso gets stretched to become larger than our observable universe Any initial small-scale roughness is smoothed to an imperceptibly small amount  Explains why the universe is so homogeneous and isotropic!

20. Consequences of cosmic inflation Any initial k constant becomes negligibly small compared with (dR/dt)2. In general relativity, k determines the geometry of space. k = 0 is Euclidean space. k=0 k<0 k>0 • Inflation predicts k=0 as now observed to 1% accuracy!

21. Consequences of cosmic inflation Quantum fluctuations of the spin-0 force-carrier that drives inflation lead to very weak fluctuations of density after inflation. Similar to Hawking radiation from black holes! Black holes make virtual particles become real! Inflation makes virtual particles become real, then stretches their waves! (The key feature of both is an “event horizon”.) e- e+ BH

22. After a few billion years… Exponential stretching causes the quantum waves to behave classically (roughly, Heisenberg’s uncertainty is relatively unimportant for very big things) The waves push around matter and radiation, creating small ripples which then amplify into all structure we see in the universe

23. Cosmic Microwave Background Radiation Maps: Observation, Theory Simulated map at WMAP resolution made in 1995 (different false color scheme, statistical comparison only) WMAP’s results were judged the top scientific breakthrough of 2003!

24. CMBR Angular Power Spectrum:Cosmic SonogramTop: Temperature fluctuations vs. angular scale(data points and theory)Bottom: Cross-correlation of temperature and linear polarizationvs. angular scaleFrom Bennett et al. 2003, WMAP

25. Conclusions • Cosmic inflation refines the big bang theory. • It’s predictions have so far been well confirmed; no other theory has explained all that inflation does. • Results suggest a new very high mass spin-0 field existed in the early universe. • Success increase confidence that we can understand the universe from age 10-35 to 10+17 seconds. • Dark matter should be produced in the lab AND detected from space “mañana.”

26. For additional information The Fabric of the Cosmos: Space, Time, and the Texture of Reality, Brian Greene The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory, Brian Greene (more advanced than The Fabric of the Cosmos) The First Three Minutes: A Modern View of the Origin of the Universe, Steven Weinberg (a slightly outdated classic) The Inflationary Universe: The Quest for a New Theory of Cosmic Origins, Alan H. Guth (advanced but without math)